The invention relates to a biaxially oriented and thermofixed multilayer film of thermoplastic polyesters with different melting points, having at least one essentially scratch-free surface.
Scratch-free films of especially high quality are required for optical applications, this being understood in particular to mean films for reprographic purposes or films for covering window glass, but carrier films which are essentially free of disturbing scratches are also required for application of metal coatings or magnetic coatings.
To produce scratch-free films, a production technology is normally used in which relative motion between the film strip and any rollers in the machine is suppressed during the entire manufacturing process of the film. In addition, friction between the individual film layers on the roll must be absolutely avoided. These requirements make it necessary to mount expensive attachments to production machinery, but nevertheless scratching of the film and consequently useless products occur especially during lengthwise stretching over rollers.
Scratches which render use of the film impossible also occur during subsequent processing of the films by customers.
The object of the present invention is to eliminate the problems involved in manufacturing scratch-free films by producing a film in which it is possible both to remove any scratches produced during film manufacture by a simple after-treatment integrated into the process, thus producing a perfect film surface, and also to produce a film with self-healing effects for any scratches that may occur during subsequent processing.